There has been much interest in membrane bioreactors (MBRs) in the water-world in recent years. MBR is a combination of two basic processes—biological degradation and membrane separation—into a single process where suspended solids and microorganisms responsible for biodegradation are separated from the treated water by membrane filtration unit. To date research has concentrated on the applicability of MBRs for domestic, industrial and mixed domestic and industrial waste-water treatment plants, concentrated flows from industrial production processes, the treatment of percolate water from waste disposal sites and the dewatering of sludge. The success of membrane bioreactors for wastewater applications led to a study of the application of MBR concepts in the drinking water production process.
In wastewater MBR-applications biological treatment in a reactor is combined with physical treatment by membrane filtration. By using membrane filtration instead of a settling process, high sludge loads can be maintained in the reactor, which (theoretically) lead to high biological degradation rates with a low sludge production. Sludge concentrations of 15-20 g/l are mentioned in the MBR-literature. The high efficiency of the process would make it possible to process highly concentrated flows and to design systems with a small footprint. In practice, the footprint is reduced by the smaller area required for the membrane filtration due to a maximal maintainable sludge concentration of 8-12 g/l and dispensing with a settlement tank. In addition higher sludge production rates have been registered than in conventional settlement systems.
JP 2003-135939A discloses a separation membrane manufactured by forming the porous resin layer on the surface of the porous base material composed of an organic fiber, part of a resin forming the porous resin layer being infiltrated into at least the surface layer part of the porous base material to form a composite layer with the porous base material at least in the surface layer part.
JP 2003-144869A discloses a separation membrane having a porous resin layer formed on the surface of the porous base material and a combined layer formed by integrating a part of a resin forming the porous resin layer with the porous base material, the pores satisfying the relationship: 2 dB≦dA (wherein dA is the average pore diameter on the surface of the side of the liquid to be treated; dB is the average pore diameter on the surface of the side of the permeated liquid) are formed on both surfaces of the porous resin layer.
JP 2001-321645A discloses a filter membrane element in which flow path materials are arranged on both the surface of a support plate and liquid separation membranes for removing impurities in the liquid above the flow path materials, the filter member element having a gap for water collection penetrating both surfaces of the support plate on a portion of the support plate; and a gap for water collection being arranged in the direction of a takeout port of the permeated water and communicating with the exit port of the permeated water.
U.S. Pat. No. 4,871,456 discloses a flat-plate laminated filter cartridge, comprising at least one filtering unit, in which said filtering unit comprises: an inner rim; an outer member surrounding an outer periphery of and spaced apart from said inner rim; upper and lower filtering films extending between said inner rim and said outer member and each having an entire inner periphery which is bonded to said inner rim, and an entire outer periphery which is bonded to at least one of another said outer periphery and said outer member so as to form a space therebetween serving as a path of a solution to be filtered; and at least one film supporting member made of one of paper, unwoven cloth and net, disposed on at least one of both sides of said upper and lower filtering films, and between said upper and lower filtering films. U.S. Pat. No. 4,871,456 further discloses that the filtering film supporting member is not at all bonded to the upper and lower filtering films and it is provided only to support the filtering films from inside.
U.S. Pat. No. 5,482,625 discloses a filtration membrane module submerged with a processed liquid in a processing tank comprising: a plurality of flat, rigid membrane cartridges vertically placed in parallel to each other as properly spaced from the adjoining membrane cartridges; cleaning stream generating means for supplying a flow parallel to the membrane surfaces of the membrane cartridges which opposes to gaps defined between the membrane cartridges opposite to each other; and sucking means for sucking permeated liquid in each membrane cartridge which is communicated with the passage of permeated liquid in each membrane cartridge; each membrane cartridge having a membrane supporting plate and a filtration membrane covering the outer surface thereof; and the membrane supporting plate supporting the filtration membrane is being made hollow by using a rigid structural member, the inside of the plate forming a passage of permeated liquid, the membrane supporting plate having an opening formed on the surface opposite to the filtration membrane the opening communicating to the passage of permeated liquid. The membrane cartridges can be membrane bags as illustrated in FIG. 27.
WO 03/037489A discloses a filtration-module for the cleaning of waste-water with a multiplicity of filtration membrane pockets each having at least one opening for the dewatering of its interior space and which are disposed vertically, parallel to one another and preferably at the same spacing to one another in a rigid holder and so arranged that the intervening spaces lying between neigboring filter membrane pockets are intensively traversed by a liquid, characterized in that the filter membrane pockets are configured to be substantially flat and flexible and on opposite sides are fixedly connected with the holder which has at least one suction line for carrying off liquid drawn through the filter membrane pocket opening, and in that the filter membrane pockets have a flexible liquid permeable core and/or a plurality of flexible permeable core elements.
JP 11-244672A discloses an element with longitudinally long permeate flow passage materials which are relatively flexible and allow the passing of the permeate and flat members disposed along both sides thereof, sealing parts being formed by tightly adhering the peripherally marginal three sides at the top end and both right and left ends thereof to constitute the quadrilateral flat planar membrane formed as a bag form. JP 11-244672A further discloses that the one side at the unsealed peripheral edge of the flat planar membrane installed with the membrane supporting member is superposed by about 1.5 cm in height on the surface on both sides of the upper part of the membrane supporting member and is welded to the membrane supporting member to support the flat planar membrane; that the heads larger in thickness than the membrane supporting member are formed at both ends of the membrane supporting member; and that both of the heads are provided with the nozzles which are communicated with the flow passages of the membrane supporting member and are used to take out the permeate.
U.S. Pat. No. 5,275,725 discloses in a second embodiment the forming the flat membrane support by casting a solution of the membrane-forming polymer on the surfaces of a membrane support and immersing the support in a suspended solidifying bath to form the semipermeable membrane parts by the so-called phase inversion method, wherein the permselective membranes can be bonded to the support by the anchoring effect wherein the penetration of the membrane-forming polymer solution into the nonwoven fabric constituting the surface layer of the support is arrested by the fibers after the gelation.
The membrane plates (filter pockets, bag with four-sided flat planar membrane) of the above-mentioned prior art are formed by bringing together the separate constituents (two membranes, spacer and support) and the two membranes are placed with their membrane supports opposite one another and a spacer is placed between them creating a gap. The resulting weak points of these concepts including the large number of construction steps; poor adhesion of the membrane to the module support resulting in detachment and stripping of the membrane; and operational problems due to the impossibility of back-flushing the membranes with sufficient pressure, as a result of the poor adhesion of the membranes to their supports, were addressed in WO 2006/056159A and WO 2006/015461A.
WO 2006/056159A discloses a frameless plate-shaped filter element, particularly for filtering fluid media, comprising outer filter layers and at least one layer of membrane material wherein between the outer filter layers at least one inner layer is provided that comprises at least on one face a plurality of bumps that are distributed across the face and mounted at a spacing from each other, the end surfaces of which bumps form a contact surface for an outer fluid-permeable layer. The attachment of the membrane layer to the reinforcing structure is however poor resulting in low backflush pressures that can be used.
CA 2 552 533A1 discloses a filter medium with at least one filter membrane which has a fabric ply as the support and protective layer, characterized in that at least one other filter membrane with another fabric ply is present as the support and protective layer, that between the two adjacent filter membranes a third fabric ply extends, and that the two adjacent filter membranes are connected to one another via threads of the two other fabric plies which extend through the third fabric ply.
WO 2006/015461A discloses an integrated permeate channel (IPC) membrane, comprising a permeate channel consisting of a spacer fabric having an upper and a lower fabric surface tied together and spaced apart by monofilament threads at a predefined distance, said permeate channel being interposed between two membrane layers, wherein said membrane layers are linked at a multitude of points with said upper and lower fabric surfaces. IPC membrane cartridges have a high resistance to backflush pressures thereby increasing their efficiency and WO 2006/015461A further discloses that it is possible to obtain an asymmetric spacer fabric-reinforced membrane with different pore size characteristics at both sides by applying different conditions on both sides of the dope coated spacer fabric.
However, WO 2006/015461A discloses the following manufacturing steps:                Spacer fabric preparation step: spacer fabric (knitted, woven or non/woven) unwinding; spacer fabric guiding into vertical position and spacer fabric spreading to prevent fold formation (perpendicular to the fabrication direction);        Spacer fabric coating step: simultaneous double-side coating of dope with a double-sided coating system and automatic dope feeding on both sides of the spacer fabric (same level at both sides) to obtain a dope coated spacer fabric;        Surface pore formation step: contacting of the double-side coated spacer fabric with water vapour phase. It is also possible to obtain an asymmetric spacer fabric-reinforced membrane with different pore size characteristics at both sides by applying different conditions on both sides of the dope coated spacer fabric.        Bulk formation step: coagulation of product into a hot water bath;        Post-treatment step: washing out of chemicals in a water reservoir; and        Drying step: drying of the product.WO 2006/015461A also discloses the preferred presence of a sealant at the perimeter of the planar membrane arranged to prevent direct fluid movement from or to the permeate channel without passing through a membrane layer. Moreover, in the single exemplification of the use of IPC-membranes disclosed in WO 2006/015461A (Application 1) a sealant such as epoxy/polyurethane, any rubber or a hot melt or even welding was deemed necessary to close at least two (preferably opposite) edges of the IPC-MBR membrane 1. Individual sealing of the IPC-membrane requires considerable manutention for a single IPC-membrane meaning high production costs. Moreover, the presence of a sealant reduces the efficiency of the filtration process by creating a blind area thereby reducing the filtration efficiency. Moreover, the sealing of membrane cartridges made from an IPC membrane can constitute a weak point, which places a limit on the allowable backflush pressure.        
The production technology for IPC-membranes disclosed in WO 2006/015461A1 does not lend itself to large-scale production thereof. Wide-scale application of IPC-membranes in membrane bioreactors, in water filtration and waste water purification depends upon the development of manufacturing technology capable of large-scale production of IPC-membranes with resulting economies of scale. Furthermore, it is desirable that the pores in the membranes be asymmetric with pores with a larger opening at the membrane-integrated permeate channel interface than at the outermost surface of the membranes.
It is therefore desirable to develop manufacturing technology capable of large-scale production of IPC-membranes with resulting economies of scale without qualitative degradation of the resulting IPC-membranes.